Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
Post subject: De-embedding lossy transmission line Posted:
Wed Jul 25, 2007 4:40 pm
Joined: Wed Jul
25, 2007 4:23 pm
Hi all experts ,
the following experiment:
I have a system which consists of
a pair of SMA cables, backplane with microstrip differential pair and
another pair of cables which S-parameters I'm trying to find.
Unfortunately, I can't just measure S-parameters of the second pair
of cables by using a VNA. But I have S-parameters of the whole system:
[SMA cables - backplane - cables], and S-parameters of [SMA cables]
and [backplane] separately. The backplane is relatively ‘lossy’ at high
I'm converting S-parameters to T-parameters,
then taking T[backplane]^-1*T[SMA-cables]^-1*T[whole system]. Then,
I’m converting back to S expecting to get "second" cables S matrix.
Beyond some frequency (~12GHz), I'm getting very high gain and obviously
wrong behavior. I used this technique in the past to de-embed NOT very
What could be wrong?
Thanks a lot in advance,
Post subject: Posted: Thu
Jul 26, 2007 3:39 am
Joined: Fri Feb 17,
2006 12:07 pm
Location: London UK
time I encountered something similar, where a VNA plot turned to rat
doo-dooz above a certain frequency, it turned out to be an unexpected
resonance. This produced a rapid variation in S parameters around the
resonant frequency, and at harmonics of it.
Is there any chance
your set-up could exhibit a resonance?